Geoff Boycott has expressed fears for Michael Vaughan's future because of the England captain's struggle to recover from recurring knee problems.

Chairman of selectors David Graveney insists Vaughan is progressing even though no comeback date has been set.

Ex-England batsman Boycott said in his BBC Sport column: "You can put as much spin on it as you want - it's worrying.

"It must be a worry because while you expect selectors to be upbeat and say he'll be all right, time's getting on."

Boycott says the history of problems Vaughan has had and the slow pace of his recovery suggests there is reason for concern.

The Yorkshire star broke down early in England's first warm-up match on their tour of India in February.

I'm surprised somebody as intelligent as Michael hasn't been to see Richard Steadman in America

That came after he was forced to go home before the one-dayers in Pakistan to undergo surgery in December.

"He hasn't completed a game since the tour of Pakistan, which is getting on for five or six months now," Boycott explained.

"If you're a fast bowler banging your foot down you'd expect to have a bit of knee trouble later on in life, a bit of arthritis or something.

"Even as a batsman you're twisting and turning when you're fielding so you might get some knee trouble later in life but you would not expect it at the age of 31."

High-profile footballers such as Alan Shearer, Henrik Larsson and Patrik Berger have turned to Colorado surgeon Dr Richard Steadman for help with knee injuries and Boycott is surprised Vaughan has not done the same.

"So many footballers have been to him - I'm surprised somebody as intelligent as Michael hasn't done that," he said.